A torque converter is well known that has a pump vane wheel, a turbine vane wheel, and a stator vane wheel rotatably disposed between the turbine vane wheel and the pump vane wheel. In such a conventional torque converter, the stator vane wheel is coupled to a non-rotating member through a one-way clutch and the torque converter has no variable displacement property. Generally, it is desired that the fluid property of a torque converter shows a high displacement (displacement coefficient) when the torque converter is fuel-efficiency oriented. However, in the conventional structure, the fluid property is univocally determined by the shapes of the pump vane wheel, the turbine vane wheel, and the stator vane wheel and, therefore, the fluid property becomes same regardless of running pattern and simultaneous improvement of the fuel efficiency performance and the motive power performance is limited.
Whereas, as described in Patent Document 1, a variable-displacement torque converter has been proposed that includes a braking means disposed between a stator vane wheel and a non-rotating member and whose displacement is varied by adjusting the braking torque of the braking means. According to this, continuous- or multi-step variation of each of the torque ratio and the displacement coefficient of the torque converter is enabled by adjusting the braking torque using the braking means. Therefore the optimal torque ratio and the optimal displacement coefficient can be set corresponding to driving conditions and running conditions. Therefore, the running performance of a vehicle can be improved.
Patent Document 1: Japanese Laid-Open Patent Publication No. 1-169170